Fanless or passively cooled computers provide many benefits over computers that use fans for cooling including increased reliability and lower maintenance costs. Fanless computers never suffer from unreliability or damage due to fan failure. One such fanless computer with an integrated display is described in U.S. Pat. No. 7,072,179. The computer of the '179 patent uses a natural convection process that results in very light air inflow and almost completely eliminates internal dust build-up and failures that result from dust build-up. As a result, maintenance costs associated with protecting components from fan failures, repairing and replacing fans, and repairing and replacing components damaged by fan failures are eliminated. Because the computer is fanless, it is also silent. Therefore, it is suitable for many applications including use in hospitals, libraries, or any other location where the presence of noise and dust is a concern. Furthermore, it comprises an integrated display so it is very compact and suitable for use in locations where the availability of space is a concern.
The computer of the '179 patent comprises a unique heat sink that supports the entire enclosure and causes heat in the device to dissipate through vents. The motherboard assembly attaches directly to the heat sink to facilitate thermal transfer characteristics so that components are cooled without the need for a fan. The heat sink further serves as the entire supporting structure of the circuit board assembly and is designed and incorporated into the device so that any stress experienced by the heat sink is not transferred to the solder joints. The entire PCB assembly moves with the heat sink.
Although operation of the integrated display computer of the '179 patent is not compromised by fan failures, the ICs thermally attached to the heat sink can use enough power to raise the heat sink temperature beyond acceptable safety limits. Therefore, there is a need to control power usage of the ICs in the fanless computer to limit the maximum heat sink temperature. Some ICs have the ability to sense their temperature and adjust their power level to keep from overheating. However, the temperature is measured at the IC, which does not directly correlate to the resulting passive heat sink temperature when the ICs and heat sink are thermally coupled. Therefore, an additional algorithm is needed that uses the temperature sensing and throttling capabilities of the ICs to prevent the passive heat sink from rising above a maximum temperature.